Cameras are prevalent in smartphones and other devices that are relatively thin. The camera flash is frequently formed of one or two phosphor-converted LEDs. The combined area of the LEDs typically determines the instantaneous brightness of the flash for a given driving current pulse. The bare LED die is GaN-based and emits blue light, and the phosphor adds a yellow component (or red and green components) so the combination of the blue light leaking through the phosphor and the phosphor light creates the bright white light for the flash.
The camera typically uses a Fresnel lens or other type of molded plastic lens to collimate the light in an attempt to direct most of the light at the subject in the camera's field of view.
Lenses cause some back reflection, which is substantially absorbed by the flash module. Lenses are relatively thick, and the distance from the top of the lens to the LED die surface depends on the footprint of the LED die. Since relatively large LED die sizes are used to obtain the required brightness with the fewest LED dies, the lens must be fairly thick. Further, the lenses generally create a conical emission pattern which does not correspond to the rectangular field of view of the camera. Accordingly, the prior art LED flash modules for cameras are relatively thick and illuminate a large area beyond the field of view of the camera, wasting such light energy.
What is needed is an LED camera flash module that is thinner than the prior art flash modules and produces a beam that more closely matches the aspect ratio of the camera's field of view.